There exists a lens-fixing technique that has already been known for about fifty years and that consists in using flexible rim elements, in general a strand of nylon thread or of steel wire, surrounding some portion of each lens. That technique is attractive because of the effects of lightness and of inconspicuousness that it procures for a person who wears spectacles equipped in this way.
However, manufacturers have had to address the difficult problem of ensuring that such flexible elements are secured to the spectacles frame, and various solutions have been proposed.
Numerous solutions make provision to bore through the frame to enable the flexible filament (thread or wire) to pass through and to enable the end of the filament to be locked either by an extra thickness of filament (see for example Documents FR-A-2 504 694, FR-A-2 489 970, U.S. Pat. No. 2,516,549, and FR-A-1 156 468), or by knot (see for example Documents U.S. Pat. No. 2,516,549, FR-A-2 506 958, FR-A-2 701 573, EP-A-0 643 316), or else by offsetting the filament once (see Document GB-A-775 293), or twice using a two-hole technique (see for example Documents FR-A-1 094 381, FR-A-1 270 904, FR-A-2 509 058, FR-A-2 524 656, FR-A-2 530 038, EP-A-0 027 415). Document FR-E-73 293 also combines a plurality of those solutions. Document EP-A-0 093 108 proposes a variant in which each end of the filament has extra thickness force fitted into a groove in the frame, which groove is provided with an abutment at each of its ends to snap-fasten the extra thickness.
Those solutions for fixing the lenses are costly and difficult to implement because a considerable degree of accuracy is required to avoid any slack which would allow the lens to fall out. In addition, any adjustment involves difficult and tedious manipulation.
Moreover, if it is desired to use a frame whose structure is made of metal wire, e.g. titanium wire, there is not enough material available in which to machine a channel through which the end of the wire can pass. That is why wire frame spectacles are presently fixed by clamping (see Documents U.S. Pat. No. 718,363 and U.S. Pat. No. 2,588,505) or more often by screwing, the lenses then being provided with holes (see Documents U.S. Pat. No. 943,085, U.S. Pat. No. 962,549, U.S. Pat. No. 5,073,020, EP-A-0 554 341).